Multi-led structures

ABSTRACT

A multi-LED structure comprises a first LED and a separate second LED disposed on a common multi-LED native substrate. The LEDs each comprise a common first layer having a cantilever portion and a base portion and a common second layer having a light-emitting emission portion disposed only over the base portion. An LED electrode electrically connects the first LED to the second LED. The cantilever portion extends in a direction different from the base portion or a length of the cantilever portion is less than a distance between the emission portions of the first and second LEDs.

CROSS REFERENCE TO RELATED APPLICATION

Reference is made to U.S. patent application Ser. No. 16/778,948, filedJan. 31, 2020, entitled Micro-LED Color Display with Different CurrentDensities by Bower et al., the disclosure of which is incorporatedherein by reference in its entirety.

TECHNICAL FIELD The present disclosure relates to micro-light-emittingdiode structures for transfer printing. BACKGROUND

Large-format inorganic light-emitting diode (iLED) displays are used inoutdoor and stadium displays. Because the iLEDs are relatively large,for example one square millimeter, they are restricted to relativelylow-resolution displays. However, as iLED technology develops, there isincreasing interest in applying smaller iLEDs to displays having higherresolution. Full-color displays typically include pixels with three (ormore) emitters, usually red, green, and blue emitters, distributed in anarray over the display surface. For example, inorganic light-emittingdiodes used in flat-panel displays are disclosed in U.S. Pat. No.9,818,725 entitled Inorganic-Light-Emitter Display with Integrated BlackMatrix.

Inorganic light-emitting diodes are semiconductor light sources relyingon p-n junctions to emit light when a suitable voltage is applied acrossthe light-emitting diode. The color of the light emitted from the iLEDcorresponds to the energy bandgap of the semiconductor. Thus, differentsemiconductor materials can emit different colors of light whenstimulated with suitably different voltages. Typical materials includeInGaN (emitting blue light), AlGaP (emitting green light), and AlGaAs(emitting red light), among many other materials. Blue-light-emittingmaterials can emit light at voltages ranging from 2.5-3.7 volts,green-light-emitting materials can emit light at voltages ranging from1.9-4 volts, and red-light-emitting materials can emit light at voltagesranging from 1.6-2 volts, for example as taught in U.S. Pat. No10,453,826, entitled Voltage-Balanced Serial ILED Pixel and Display.Moreover, the efficiency with which the different materials emit lightcan depend on the density of the current passing through the materials.

In order to provide the different voltages and currents needed by thedifferent light-emitting diodes emitting different colors of light in afull-color pixel, a separate power supply can supply power, ground, andcontrol signals to each color light emitter in each multi-color pixel.By supplying the appropriate voltages and currents to each lightemitter, the light emitters efficiently emit light. However, providingthree (or more) different power, ground, and control signals to eachmulti-color pixel requires three times as many power supplies, lines,and connections, reducing the available space in the display andincreasing costs.

Alternatively, a single power supply can provide power to all threedifferent iLEDs in the full-color pixels. In this case any excessvoltage is dropped across other circuit components, increasing heat andreducing overall display system power efficiency.

There is a need, therefore, for an improved pixel and LED structure thatimproves power efficiency and reduces circuitry, wiring, and assemblycosts.

SUMMARY

According to some embodiments of the present disclosure, a multi-LEDstructure comprises a multi-LED native substrate and a patternedsemiconductor layer comprising semiconductor portions disposed on orover the multi-LED native substrate. The multi-LED native substrate canbe a single, unitary, and contiguous substrate on which is disposed thesemiconductor portions. In some embodiments, the multi-LED nativesubstrate is not divided into separate or distinct portions (e.g., eachportion comprising a separate and independent individual semiconductorportion) that can be separately disposed in different locations and istherefore a single, unitary, and contiguous substrate. The semiconductorportions define at least a first LED and a second LED separate from thefirst LED. The first LED and the second LED each comprise (i) a firstlayer having a cantilever portion and a base portion, and (ii) a secondlayer disposed only over the base portion of the first layer andcomprising an emission portion. In some embodiments, at least a portionof the first layer is shared between the first LED and the second LED.In some embodiments, at least a portion of the first layer is at least aportion of the multi-LED native substrate. An LED electrode is disposedon at least a portion of the multi-LED native substrate or disposed onat least a portion of a non-semiconductor structure in the semiconductorlayer, or both. The LED electrode is also disposed on at least a portionof the first LED and on at least a portion of the second LED so that theLED electrode electrically connects the first LED to the second LED. Insome embodiments, the cantilever portion of the first LED extends in afirst direction and the base portion of the first LED extends in asecond direction different from the first direction. In someembodiments, the cantilever portion of the first LED has a firstcantilever length, the cantilever portion of the second LED has a secondcantilever length, and an LED emission separation distance between theemission portion of the first LED and the emission portion of the secondLED is less than or equal to the first cantilever length and less thanor equal to the second cantilever length. In some embodiments, both aretrue. The first LED and the second LED can be electrically connected inserial or electrically connected in parallel. The multi-LED structurecan comprise more than two semiconductor portions and LEDs that areelectrically connected in any combination of series and parallel for anycombination of LEDs. For example, the semiconductor portions can defineat least a third LED separate from the first LED and separate from thesecond LED. Separate LEDs have independent emission portions that can bespatially separate or electrically separate in the absence ofelectrodes. Separate LEDs can share at least a portion of a cantileverportion or can have separate cantilever portions. The first LED and thesecond LED can have any one or combination of substantially the samesize, substantially the same area over the multi-LED substrate, anddifferent size or same size light-emitting areas of the first LED andthe second LED.

The multi-LED structure can comprise a tether or a broken or fracturedtether. In embodiments, the first and second LEDs do not comprise atether or portion of a tether. The multi-LED structure can be transferprinted, for example micro-transfer printed. The multi-LED structure canbe a bare die without an enclosing package, e.g., a ceramic or plasticpackage.

According to embodiments of the present disclosure, the multi-LED nativesubstrate has a surface and the first direction of the cantileverportion is orthogonal to the second direction of the base portion andboth the first and the second directions are substantially parallel tothe surface. According to some embodiments, the cantilever portionextends in a same direction as the base portion. According to someembodiments, the first LED and the second LED extend in substantially asame direction. According to some embodiments, the first LED and thesecond LED extend in substantially orthogonal directions.

According to embodiments of the present disclosure, the multi-LEDstructure can comprise a first LED contact disposed on the first LED anda second LED contact disposed on the second LED, the first LED contactand the second LED contact separate from the LED electrode and notelectrically connected to the LED electrode. The LED contact separationdistance between the first and second LED contacts separate from the LEDelectrode can be greater than a first LED length of the first LED,greater than a second LED length of the second LED, or greater than thelarger of the first LED length and the second LED length. A length of anLED can be the longest dimension of the LED parallel to a surface of themulti-LED native substrate. The separate first and second LED contactscan be electrically connected to an external device through wiresseparate from the LED electrode. For example, the multi-LED structurecan be disposed on a target substrate having target substrate wires thatare electrically connected to the separate first and second LEDcontacts, for example using photolithographic methods and materials.

According to some embodiments of the present disclosure, the multi-LEDnative substrate has a center, a first edge, and a second edge differentfrom the first edge. In some embodiments, the first LED contact separatefrom the LED electrode is disposed closer to the first edge than to thecenter and the second LED contact separate from the LED electrode isdisposed closer to the second edge than to the center. In someembodiments, the multi-LED native substrate has a center, a firstcorner, and a second corner different from the first corner, and thefirst LED contact separate from the LED electrode is disposed closer tothe first corner than to the center and the second LED contact separatefrom the LED electrode is disposed closer to the second corner than tothe center.

According to some embodiments, the multi-LED native substrate is a firstmulti-LED native substrate and the multi-LED structure comprises asecond multi-LED native substrate disposed on the first multi-LEDsubstrate, comprises other LEDs separate and independent of the firstand second LEDs disposed on the second multi-LED native substrate, orcomprises both. The one or more LEDs (first and second LEDs) disposed onthe first multi-LED native substrate and the other LEDs separate andindependent of the first and second LEDs disposed on the secondmulti-LED native substrate comprise a semiconductor material differentfrom a semiconductor material of the semiconductor layer, and can, forexample can emit different colors of light than the first and secondLEDs can emit.

According to some embodiments, one or more other LEDs separate from thefirst LED and separate from the second LED are disposed on the firstmulti-LED native substrate. The one or more LEDs (first and second LEDs)disposed on the first multi-LED native substrate and the other LEDsseparate and independent of the first and second LEDs disposed on thefirst multi-LED native substrate comprise a semiconductor materialdifferent from a semiconductor material of the semiconductor layer, andcan, for example can emit different colors of light than the first andsecond LEDs can emit.

According to some embodiments, the multi-LED native substrate comprisesat least a portion of the first layer or the first layer comprises atleast a portion of the multi-LED native substrate and the multi-LEDnative substrate is electrically conductive.

According to embodiments of the present disclosure, a multi-LEDcomponent structure comprises a component substrate and a firstmulti-LED structure is disposed on the component substrate. Themulti-LED component structure can comprise a second multi-LED structuredisposed on the component substrate, can comprise one or more other LEDsdisposed on the component substrate, or can comprise both. In someembodiments, the first multi-LED structure and the second multi-LEDstructure can emit different colors of light. In some embodiments, thefirst multi-LED structure and the one or more other LEDs emit differentcolors of light. The first LED and the second LED of the first multi-LEDstructure can be electrically connected in series and the first LED andsecond LED of the second multi-LED structure can be electricallyconnected in parallel.

For example, the first multi-LED structure can emit red light and thesecond multi-LED structure can emit green or blue light.

According to some embodiments, the multi-LED structure comprises a thirdindividual and separate LED separate from the first and second LEDs ofthe multi-LED structure or a third multi-LED structure disposed on thecomponent substrate and the third LED or third multi-LED structure emitsa color of light different from a color of light emitted by the firstand second LEDs of the first multi-LED structure and different from acolor of light emitted by the one or more other LEDs or second multi-LEDstructure. According to some embodiments, the multi-LED componentstructure comprises another LED or second multi-LED structure disposedon the component substrate, a third LED or third multi-LED structuredisposed on the component substrate, and a fourth LED or fourthmulti-LED structure disposed on the component substrate. The one or moreother LEDs or second multi-LED structure, the third LED or thirdmulti-LED structure, and the fourth LED or fourth multi-LED structurecan be electrically serially connected. According to some embodiments,the second LED or second multi-LED structure emits a second color oflight, the third LED or third multi-LED structure emits a third color oflight, and the fourth LED or fourth multi-LED structure emits a fourthcolor of light and the second, third, and fourth colors of light are alldifferent. The second color of light can be red, the third color oflight can be green, and the fourth color of light can be blue.

According to some embodiments, an LED wafer comprises a wafer comprisingsacrificial portions separated by anchor portions and a multi-LEDstructure is disposed entirely and completely over each sacrificialportion and each multi-LED structure is physically connected to ananchor with a tether.

According to some embodiments of the present disclosure, a method ofmaking a multi-LED structure comprises providing a multi-LED nativesubstrate and disposing semiconductor layers on the multi-LED nativesubstrate. The semiconductor layers are patterned to form spatiallyseparated semiconductor portions. The semiconductor portions define atleast a first LED and a second LED separate from the first LED. Thefirst LED and the second LED each comprise a first layer having acantilever portion and a base portion. A patterned second layer isdisposed only over the base portion. An LED electrode is disposed on atleast a portion of the multi-LED native substrate or on at least aportion of a non-semiconductor structure in the semiconductor layer. TheLED electrode is also disposed on at least a portion of the first LEDand on at least a portion of the second LED, so that the LED electrodeelectrically connects the first LED to the second LED. In someembodiments, the cantilever portion of the first LED extends in a firstdirection and the base portion of the first LED extends in a seconddirection different from the first direction. In some embodiments, thecantilever portion of the first LED has a first cantilever length, thecantilever portion of the second LED has a second cantilever length, andan LED emission separation distance between the emission portion of thefirst LED and the emission portion of the second LED is less than orequal to the first cantilever length and less than or equal to thesecond cantilever length. In some embodiments, both are true.

Methods of the present disclosure comprise providing an LED source wafercomprising sacrificial portions separated by anchor portions. Amulti-LED structure is disposed entirely and completely over eachsacrificial portion and each multi-LED structure is physically connectedto an anchor with a tether. The sacrificial portions are etched tosuspend each multi-LED structure over a corresponding sacrificialportion. A stamp and a target substrate are provided, and each multi-LEDstructure is micro-transfer printed from the multi-LED native substrateto the target substrate with the stamp.

According to an embodiment of the present disclosure, a multi-LEDstructure comprises an electrically conductive semiconductor layercomprising a cantilever portion and two or more spatially separated baseportions, a separate emissive portion comprising a light-emissivesemiconductor portion disposed on each base portion, and an LED contactpad disposed on each emissive portion. Each emissive portion emits lightwhen electrical power is provided to the cantilever portion and the LEDcontact pad.

According to some embodiments of the present disclosure, a multi-LEDcomponent structure comprises a component substrate, a first multi-LEDnative substrate disposed on the component substrate, the firstmulti-LED native substrate having a first LED and a separate second LEDdisposed thereon, wherein the first LED and the second LED are native tothe first multi-LED native substrate and electrically connected, and asecond multi-LED native substrate having a third LED and a separatefourth LED disposed thereon, the third LED and the fourth LED are nativeto the second multi-LED native substrate and electrically connected,wherein the first LED, the second LED, the third LED, and the fourth LEDare electrically connected to a common electrical connection. At leastone of (i) the first LED and the second LED can be electricallyconnected in series and the third LED and the fourth LED can beelectrically connected in parallel and (ii) the first LED and the secondLED can emit a first color of light and the third LED and the fourth LEDcan emit a second color of light. The second multi-LED native substratecan be disposed on the first multi-LED native substrate.

According to some embodiments of the present disclosure, a multi-LEDcomponent structure further comprises a fifth LED non-native to thecomponent substrate, the first multi-LED native substrate and the secondmulti-LED native substrate, wherein the fifth LED emits a differentcolor of light from the first LED, the second LED, the third LED, andthe fourth LED.

Embodiments of the present disclosure provide a display, lamps, pixels,or light emitters having improved optical characteristics and powerefficiency and fewer separate components, control circuits, andelectrical connections that can be constructed in fewer manufacturingsteps.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, aspects, features, and advantages ofthe present disclosure will become more apparent and better understoodby referring to the following description taken in conjunction with theaccompanying drawings, in which:

FIG. 1A is a schematic cross section of a multi-LED structure takenacross cross section line A of the schematic plan view of FIG. 1Billustrating embodiments of the present disclosure;

FIG. 1C is a schematic cross section of a multi-LED structure wherein asemiconductor layer and a multi-LED native substrate comprise a samematerial according to illustrative embodiments of the presentdisclosure;

FIG. 1D is a schematic cross section of a multi-LED structure wherein afirst layer is common to multiple LEDs according to illustrativeembodiments of the present disclosure;

FIG. 1E is a schematic cross section of a multi-LED structure wherein afirst layer and a multi-LED native substrate are a common layeraccording to illustrative embodiments of the present disclosure;

FIG. 2A is a schematic perspective of an LED indicating cross-sectionline A of the cross section of FIG. 2D, FIG. 2B is a schematicperspective indicating layers of the

LED, and FIG. 2C is an exploded schematic perspective of the LEDaccording to illustrative embodiments of the present disclosure;

FIG. 3A is a schematic perspective of an LED indicating cross-sectionline A also corresponding to the cross section of FIG. 2D, FIG. 3B is aschematic perspective indicating layers of the LED, and FIG. 3C is anexploded schematic perspective of the LED according to illustrativeembodiments of the present disclosure;

FIG. 4A is a schematic perspective of an LED, FIG. 4B is a schematicperspective indicating layers of the LED, and FIG. 4C is an explodedschematic perspective of the LED according to illustrative embodimentsof the present disclosure;

FIGS. 5-23 are schematic plan views illustrating electrical connectionswithin multi-LED structures according to illustrative embodiments of thepresent disclosure;

FIG. 24A is a schematic cross section of a multi-LED structure on anative source wafer and FIGS. 24B and 24C are schematic cross sectionsof a multi-LED structure on a native source wafer with a handlesubstrate according to illustrative embodiments of the presentdisclosure;

FIG. 25 is a schematic perspective of a component comprising multi-LEDstructures and LEDs illustrating embodiments of the present disclosure;

FIG. 26 is a graph illustrating inorganic LED light output efficiencywith respect to current density useful in understanding embodiments ofthe present disclosure;

FIG. 27 is a schematic plan view and pixel detail of a displaycomprising multi-LED structures and LEDs illustrating embodiments of thepresent disclosure;

FIGS. 28-30 are schematic display pixel details comprising multi-LEDstructures and LEDs illustrating embodiments of the present disclosure;

FIG. 31 is a schematic diagram of an active-matrix display comprisingmulti-LED structures illustrating embodiments of the present disclosure;

FIG. 32 is a schematic perspective of an active-matrix display accordingto illustrative embodiments of the present disclosure;

FIG. 33 is a schematic plan view illustrating reverse-bias electricalconnections within multi-LED structures according to embodiments of thepresent disclosure;

FIG. 34 is a schematic perspective of an individual LED disposed on amulti-LED native substrate of a multi-LED structure according toillustrative embodiments of the present disclosure;

FIG. 35 is a schematic perspective of a multi-LED structure andindividual LEDs disposed on a multi-LED native substrate of anothermulti-LED structure according to illustrative embodiments of the presentdisclosure; and

FIGS. 36 and 37 are flow charts according to illustrative embodiments ofthe present disclosure.

Features and advantages of the present disclosure will become moreapparent from the detailed description set forth below when taken inconjunction with the drawings, in which like reference charactersidentify corresponding elements throughout. In the drawings, likereference numbers generally indicate identical, functionally similar,and/or structurally similar elements. The figures are not drawn to scalesince the variation in size of various elements in the Figures is toogreat to permit depiction to scale.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

Embodiments of the present disclosure provide electrically connectediLEDs formed at the same time with common materials in a single process,e.g., a photolithographic process. The iLEDs can have one or more of areduced area and structure size, improved manufacturing efficiency,improved operating efficiency, and simplified power and controlcircuitry when incorporated in a display or in other multi-color lightoutput devices such as lamps, or as individual structures in an opticalindicator. In some embodiments, a power supply for differently coloredlight emitters in an illumination device or display pixel can comprise asingle current supply and a single voltage supply rather than multiplecurrent and voltage supplies.

According to some embodiments of the present disclosure and asillustrated in the cross section of FIG. 1A taken along cross sectionline A of the corresponding plan view of FIG. 1B and FIG. 1C, amulti-LED structure 99 comprises a multi-LED native substrate 10 and apatterned semiconductor layer 30 comprising spatially separatedsemiconductor portions 30P (e.g., first semiconductor portion 30A andsecond semiconductor portion 30B) disposed on or over multi-LED nativesubstrate 10. A multi-LED native substrate 10 can be a single, unitary,and contiguous substrate. Semiconductor layer 30 is formed (e.g.,photolithographically patterned) on multi-LED native substrate 10 makingfirst semiconductor portion 30A and second semiconductor portion 30Bnative to multi-LED native substrate. First semiconductor portion 30Aand second semiconductor portion 30B, both native to multi-LED nativesubstrate 10, can be defined in common steps using common materials andtools. In some embodiments, multi-LED native substrate 10 is not dividedinto separate or distinct portions (e.g., each portion comprising aseparate semiconductor portion such as first semiconductor portion 30Aor second semiconductor portion 30B) that can be separately disposed indifferent locations, and is therefore a single, unitary, and contiguoussubstrate. Multi-LED native substrate 10 can comprise any suitablematerial on which semiconductor layer 30 can be formed and can include aseed layer. In some embodiments, semiconductor layer 30 comprises a seedlayer. For example, multi-LED native substrate 10 can comprise asapphire, silicon, silicon carbide, or compound semiconductor wafer,such as those found in the integrated circuit, flat-panel display, oropto-electronic arts. Multi-LED native substrate 10 can comprise anundoped semiconductor, for example undoped silicon, or an ion-dopedsemiconductor that is resistive to the flow of electrical current, e.g.,as shown in FIG. 1C with semiconductor structures shown with commonshading. First and second semiconductor portions 30A, 30B (and any othersemiconductor portions 30P) are collectively referred to assemiconductor portions 30P.

Semiconductor layer 30 and semiconductor portions 30P can be constructedby depositing epitaxial layers of semiconductor materials, for exampledoped or undoped semiconductor materials such as Si or compoundsemiconductor materials such as GaN, GaAs, In_(x)Ga_(1-x)N,Al_(x)Ga_(1-x)P, and Al_(x)Ga_(1-x)As, or other semiconductor orcompound semiconductor materials and alloys, for example with p or ndoping, and, in some embodiments, then pattern-wise etched to formseparate semiconductor portions 30P. Semiconductor layer 30 can comprisemono-crystalline semiconductor materials and can be deposited, togetherwith any suitable dopants, for example by sputtering, evaporative, orvapor deposition methods and processed using photolithographic methodsand materials, for example using patterned photoresist masking andetching techniques. Semiconductor layer 30 can include sublayers (e.g.,first layer 31 and second layer 32) and first and second layers 31, 32can be patterned and can also include sub-layers, for example withdifferent material compositions or doping or both.

Semiconductor portions 30P (e.g., first semiconductor portion 30A andsecond semiconductor portion 30B) can define at least a first LED 20Aand a second LED 20B spatially separate from first LED 20A on multi-LEDnative substrate 10. First and second LEDs 20A and 20B are referred tocollectively as LEDs 20. First LED 20A and second LED 20B can eachcomprise (i) a first layer 31 having a cantilever portion 34 and a baseportion 36, and (ii) a second layer 32 disposed only over base portion36 of first layer 31 comprising an emission portion 33 that emits lightand is a light-emitting portion. Spatially separate LEDs 20 haveseparate emission portions 33 (and base portions 36) and can beindependently operable with suitable electrical connections. First andsecond layers 31, 32 can be semiconductor layers with or without dopingor sub-layers. First layer 31 can be separate for both first and secondLEDs 20A, 20B or, in some embodiments, first layer 31 is common (forexample at least partially common) to both first and second LEDs 20A,20B, e.g., as shown in FIG. 1D and 1E. First layer 31 can be common, forexample at least partially common, with multi-LED native substrate 10,e.g., as shown in FIG. 1E.

Referring to FIG. 1C, in some embodiments, multi-LED native substrate 10and first layer 31 are the same, or at least partially the same, layer,and cantilever portion 34 is a raised portion of multi-LED nativesubstrate 10 that extends beyond emission portion 33. First layer 31comprising cantilever portion 34 and base portion 36 is an electricallyconductive layer and does not emit light. First layer 31 conductselectrical current to second layer 32 which emits light from emissiveportion 33 in response to the electrical current. LED contact pads 26,for example comprising a photolithographically patterned evaporativelydeposited metal such as aluminum, a transparent conductive oxide, or adoped semiconductor, can be disposed on emission portion 33 andcantilever portion 34 of first and second LEDs 20A, 20B to provideelectrical contacts to first and second LEDs 20A, 20B. Electrical power(e.g., electrical current at a suitable voltage) can be provided tofirst and second LEDs 20A, 20B so that first and second LEDs 20A, 20Bemit light. LEDs 20 can be horizontal LEDs 20 and can be eithertop-emitting LEDs 20 that emit light away from multi-LED nativesubstrate 10 or bottom-emitting LEDs 20 that emit light throughmulti-LED native substrate 10.

Multi-LED native substrate 10 can be electrically conductive andelectrically connect first and second semiconductor portions 30A, 30B,for example such that sufficient electrical current can flow to providea desired amount of light output from emission portions 33. In someembodiments, for example as shown in FIG. 1D, first layer 31 can be atleast partially common to both first and second LEDs 20A, 20. In somesuch embodiments, cantilever portions 34 can be at least partiallycommon to both first and second LEDs 20A, 20 but base portions 36 andemission portions 33 are separate. In some embodiments, for example asshown in FIG. 1E, multi-LED native substrate 10 is at least a portion offirst layer 30 or is first layer 30 or first layer 30 comprises at leasta portion of multi-LED native substrate 10. In the illustrativeembodiment of FIG. 1E, first and second LEDs 20A, 20B can have a commonfirst layer 31. In some such configurations, first LED 20A separate fromsecond LED 20B means that emission portions 33 of each of first LED 20Aand second LED 20B are spatially separate, separately controllable, andwith a common electrical connection through first layer 31.

As shown in FIG. 1E, a multi-LED structure 99 comprises an electricallyconductive semiconductor layer (first layer 31, multi-LED nativesubstrate 10) comprising a cantilever portion 34 and two or morespatially separated base portions 36. A separate emissive portion 33comprises a light-emissive semiconductor portion disposed on each baseportion 36. An LED contact pad 26 is disposed on each emissive portion33. Each emissive portion 33 emits light when electrical power isprovided to cantilever portion 34 and LED contact pad 26. In someembodiments, LED electrode 38 electrically connects each LED contact pad26 so that emissive portions 33 are electrically connected in parallel.

Patterned dielectric layers 24 or dielectric structures (e.g.,comprising silicon dioxide or silicon nitride deposited by sputtering orvapor deposition and photolithographically patterned) can electricallyinsulate and environmentally protect portions of first and second LEDs20A, 20B. First and second LED electrodes 28A, 28B, for examplecomprising reflective patterned metal traces such as aluminum for abottom-emitter LED 20 or transparent conductive oxides for a top-emitterLED 20 (collectively LED electrodes 28), can be pattern-wise disposed bysputtering or vapor deposition over patterned dielectric layers 24 inelectrical contact with LED contact pads 26 to conduct electricalcurrent to first and second LEDs 20A, 20B through LED contact pads 26.FIGS. 1A and 1B illustrate two semiconductor portions 30P (definingfirst and second LEDs 20A and 20B) but embodiments of the presentdisclosure are not limited to only two semiconductor portions 30P andLEDs 20. In some embodiments of the present disclosure and asillustrated further below, semiconductor layer 30 can comprise three,four, five, six, seven, eight, nine, ten, or more semiconductor portions30P defining corresponding LEDs 20. Different LEDs 20 can have differentsizes or shapes and, optionally, be electrically connected withdifferent sizes, shapes, or arrangements of contact pads 26.

According to some embodiments of the present disclosure, multi-LEDstructures 99 have at least one of a width and a length that is nogreater than 500 microns (e.g., no greater than 200 microns, no greaterthan 100 microns, no greater than 50 microns, no greater than 25microns, no greater than 15 microns, no greater than 12 microns, nogreater than 8 microns, or no greater than 5 microns). Differentmulti-LED structures 99 can have different sizes. Multi-LED structures99 provide an advantage according to embodiments of the presentdisclosure since they are sufficiently small and can be disposedspatially close together so that different multi-LED structures 99 in apixel 60 and sub-pixel cannot be readily distinguished by the humanvisual system in a display or lamp at a desired viewing distance,improving color mixing of light emitted by a pixel 60 and sub-pixel andproviding apparent improvements in resolution and a reduction ofpixelization. Multi-LED structures 99 can also assemble multiple LEDs 20in fewer manufacturing steps and can require fewer LED packages.Multi-LED structures 99 can be unpackaged (e.g., bare) die.

The perspectives of FIGS. 2A-2C and the corresponding cross section ofFIG. 2D illustrate the detailed structure of an individual LED 20 (e.g.,first LED 20A or second LED 20B). As shown, LED 20 comprises asemiconductor layer 30 comprising first layer 31 and second layer 32.Semiconductor layer 30 can comprise a seed layer on which epitaxialsemiconductor material is disposed, e.g., by vapor deposition. Firstlayer 31 has a cantilever portion 34 and an adjacent base portion 36.Patterned second layer 32 has an emission portion 33 disposed on baseportion 36 of first layer 31. First layer 31 is electrically conductiveand second layer 32 is both conductive and light-emissive. LED contactpads 26 are disposed on each of cantilever portion 34 and emissionportion 33. FIG. 2D shows a conduction zone 39 of first layer 31 thatconducts electrical current to a recombination zone 38 of emissionportion 33 of second layer 32. Electrons and holes conducted by LEDcontact pads 26 through conduction zone 39 of conductive first layer 31and through emission portion 33 combine in recombination zone 38 to emitlight having a frequency and color corresponding to a bandgap of thesemiconductor material comprising recombination zone 38 and emissionportion 33.

FIGS. 1A-1C illustrate LED structure tethers 25 related tomicro-transfer printing multi-LED structures 99, as discussed furtherbelow, for example comprising a portion of multi-LED native substrate10, a dielectric material such as silicon dioxide or silicon nitride, oran organic material such as a photolithographically deposited andpatterned photoresist. FIGS. 2A-2D illustrate similarly constructed LEDtethers 22. However, LED tethers 22 are found on individual LEDs 20, notin multi-LED structures 99 as discussed further below and are distinctstructures from LED structure tethers 25. LEDs 20 with LED tethers 22can be individually micro-transfer printed, unlike first and second LEDs20A, 20B. LEDs 20 (e.g., first LED 20A and second LED 20B) included inmulti-LED structures 99 do not include individual LED tethers 22, sincefirst LED 20A and second LED 20B are constructed together in a commonprocess on multi-LED native substrate 10, that is are native tomulti-LED native substrate 10. Multi-LED native substrate 10 can have anLED structure tether 25 that enables the entire multi-LED nativesubstrate 10 together with first LED 20A and second LED 20B to bemicro-transfer printed from a source wafer as a complete unit. (LEDtether 22 of FIG. 2D is shown for illustration and is not properly partof cross section line A of FIG. 2A.) Printed LEDs 20 that include LEDtethers 22 can be used in combination with a multi-LED structure 99, forexample that includes an LED structure tether 25, as discussed furtherbelow.

As shown in FIGS. 1A and 1B, first LED electrode 28A is disposed on atleast a portion of multi-LED native substrate 10 or disposed on anon-semiconductor structure in semiconductor layer 30 (e.g., a portionof patterned dielectric layer 24) and is disposed on at least a portionof first LED 20A and on at least a portion of second LED 20B toelectrically connect first LED 20A to second LED 20B on multi-LED nativesubstrate 10. As shown in FIG. 1A, first LED electrode 28A is disposedon patterned dielectric layer 24 in semiconductor layer 30 and secondLED electrode 28B is disposed directly on multi-LED native substrate 10and patterned dielectric layer 24 in semiconductor layer 30. Electrodes28 can comprise a metal such as aluminum or a transparent conductiveoxide and can be made using relatively fine high-resolution lithographymethods and materials practiced in the photolithographic arts. First andsecond LED electrodes 28A and 28B can conduct electrical current toexternal electrical contacts to provide electrical power to multi-LEDstructure 99. According to some embodiments of the present disclosure,external electrical connections to LED electrodes 28 or LED contact pads26 are constructed using relative coarse, low-resolution, and lessexpensive methods and materials, for example found in the printedcircuit board arts, thereby reducing the costs of using multi-LEDstructures 99 (as compared to using high-resolution photolithographicprocessing for all connections).

In some embodiments of the present disclosure and as illustrated inFIGS. 1A and 1B, cantilever portion 34 of first LED 20A has a firstcantilever length L1, cantilever portion 34 of second LED 20B has asecond cantilever length L2, and an LED emission separation distance LSbetween emission portion 33 of first LED 20A and emission portion 33 ofsecond LED 20B is less than or equal to one or more of first cantileverlength L1 and second cantilever length L2. According to someembodiments, an LED emission separation distance LS between emissionportions 33 of two LEDs 20 is the smallest distance between emissionportions 33 of first and second LEDs 20A, 20B parallel to a surface ofmulti-LED native substrate 10. According to some embodiments, first LED20A and second LED 20B can extend in substantially a same direction, forexample in substantially parallel directions, but are not collinear (acenter line of first and second LEDs 20A, 20B are not in a common line).In some embodiments, first LED 20A and second LED 20B extend insubstantially a same direction and are collinear having collinear centerlines (e.g., within manufacturing tolerances). An LED 20 extending in adirection can refer to the direction of a longest dimension of the LED20 parallel to multi-LED native substrate 10, as shown with crosssection line A of FIG. 2A. In some embodiments, a cantilever portion 34extending in a direction refers to the direction of a longest dimensionof cantilever portion 34 parallel to multi-LED native substrate 10, asshown with cross section line A of FIG. 4A. In some embodiments, acantilever portion 34 extending in a direction refers to the directionof a cantilever portion midline from an LED contact pad 26 disposed oncantilever portion 34 towards base portion 36 parallel to multi-LEDnative substrate 10, as shown with cross section line A of FIG. 3A. Insome embodiments, a base portion 36 or emission portion 33 extending ina direction refers to the direction of a longest dimension of baseportion 36 or emission portion 33 parallel to multi-LED native substrate10, as shown with cross section line B of FIG. 3A. In some embodiments,a base portion 36 or emission portion 33 extending in a direction refersto the direction of a base portion midline (centerline) from an LEDcontact pad 26 disposed on emission portion 33 towards cantileverportion 34 parallel to multi-LED native substrate 10, as shown withcross section line B of FIG. 4A. According to some embodiments, firstLED 20A and second LED 20B can extend in different directions, forexample in substantially orthogonal directions. Similarly, according tosome embodiments, cantilever portion 34 and emission portion 33 (andbase portion 36) can extend in different directions, for example insubstantially orthogonal directions. Substantially can mean within thetolerances of a design or manufacturing process or within 10 degrees,for example with reference to parallel structures or elements.

As shown in FIGS. 3A-4C, in some embodiments of the present disclosurecantilever portion 34 of first LED 20A extends in a first direction D1and base portion 36 of first LED 20A extends in a second direction D2different from first direction D1. In some embodiments of the presentdisclosure, cantilever portion 34 of second LED 20B extends in a firstdirection D1 and base portion 36 of second LED 20B extends in a seconddirection D2 different from first direction D1. Referring to theperspectives of FIGS. 3A-3C, emission portion 33 of second layer 32 ofsemiconductor layer 30 is disposed on base portion 36 of first layer 31of semiconductor layer 30. Emission portion 33 extends as far aspossible in second direction D2 over base portion 36 of first layer 31.Referring to the perspectives of FIGS. 4A-4C, emission portion 33 ofsecond layer 32 of semiconductor layer 30 is likewise disposed on baseportion 36 of first layer 31 of semiconductor layer 30 but extends onlyas far as cantilever portion 34 in second direction D2 over first layer31. LEDs 20 can incorporate either or both of the structures of FIGS.3A-3C and FIGS. 4A-4C according to various embodiments of the presentdisclosure.

In some embodiments of the present disclosure, and as illustrated inFIGS. 3A and 4C, cantilever portion 34 of first LED 20A extends in afirst direction D1 and base portion 36 of first LED 20A extends in asecond direction D2 different from first direction D1. Similarly, insome embodiments, cantilever portion 34 of second LED 20B extends in afirst direction D1 and base portion 36 of second LED 20B extends in asecond direction D2 different from first direction D1. Cantilever andbase portions 34, 36 that extend in different directions can enable LEDs20 disposed in close proximity with reduced area over multi-LED nativesubstrate 10. In some embodiments, cantilever portion 34 extends in adifferent direction from base portion 36 and an LED emission separationdistance LS between emission portions 33 of first and second LEDs 20Aand 20B can be less than one or more of first cantilever length L1 andsecond cantilever length L2. According to some embodiments, first andsecond directions D1 and D2 can be orthogonal, as shown in FIGS. 3A-4C,and parallel to a surface of multi-LED native substrate 10.

By disposing emission portions 33 of first LED 20A and second LED 20B inclose proximity, emission portions 33 can appear as a single emittingarea to a viewer of multi-LED structures 99 of the present disclosure ata desired viewing distance, thereby reducing the apparent pixelizationof multi-LED structures 99, for example used in displays or forlighting. Such small LED emission separation distances LS in multi-LEDstructures 99 can also improve color mixing for applications in which amulti-color emitter or white light is desired. Furthermore, suchclose-proximity emission portion 33 arrangements for multiple LEDs 20can enable small light-emitting structures useful in display andillumination, improving the resolution of the displays and lamps, andcan facilitate high-density micro-transfer printing with fewer printsteps from a multi-LED structure 99 native source wafer 40 since two (ormore) LEDs 20 can be transferred in a single step, rather than requiringtwo (or more) transfer steps, one for each LED 20.

According to some embodiments of the present disclosure, first LED 20Aand second LED 20B of multi-LED structure 99 can be substantially (e.g.,within 5%) the same size, can cover substantially (e.g., within 5%) asame-size area over multi-LED native substrate 10, can havesubstantially (e.g., within 5%) the same light-emitting area of emissionportion 33, or any combination of these. In some embodiments, first LED20A and second LED 20B of multi-LED structure 99 can be different sizes,can cover different-size areas over multi-LED native substrate 10, canhave different light-emitting areas of emission portion 33, or anycombination of these. Size can be defined by any combination of length,width, or height over multi-LED native substrate 10 and area can bedefined by any combination of length or width over multi-LED nativesubstrate 10.

LEDs 20 of multi-LED structure 99 of the present disclosure can beelectrically connected in serial or in parallel, or in a combination ofserial and parallel connections. Referring to the plan view andelectrical schematic of FIG. 5 , first LED 20A is electrically connectedin parallel with second LED 20B. LED contact pad 26 of cantileverportion 34 of first LED 20A is electrically connected to LED contact pad26 of cantilever portion 34 of second LED 20B with first LED electrode28A and LED contact pad 26 of emission portion 33 of first LED 20A iselectrically connected to LED contact pad 26 of emission portion 33 ofsecond LED 20B with second LED electrode 28B. Both first and second LEDelectrodes 28A and 28B are partially disposed on a portion of multi-LEDnative substrate 10 or non-semiconductor structure (e.g., patterneddielectric layer 24 as shown in FIG. 1A) between first and second LEDs20A, 20B. First and second electrodes 28A and 28B can be contacted byexternal power sources, for example through electrodes connected tofirst and second electrodes 28A, 28B. Emission portions 33 of first andsecond LEDs 20A, 20B are separated by an LED emission separationdistance LS less than a cantilever length L. A third LED 20, or moreLEDs 20, can be similarly arranged on multi-LED native substrate 10 on aside of second LED 20B opposite first LED 20A and electrically connectedin parallel with first and second LEDs 20A, 20B using first and secondelectrodes 28A, 28B. LED structure tether 25 can be physically connectedto LED substrate 10 to enable, or as a consequence of, micro-transferprinting multi-LED structure 99.

FIGS. 1D and 1E illustrate embodiments in which first and second LEDs20A, 20B are electrically connected in parallel. In some suchconfigurations, a separate electrode to electrically connect cantileverportions 34 is not necessary, since first and second LEDs 20A, 20B shareat least a portion of common first layer 31 that provides a commonelectrical connection to emission portions 33 of first and second LEDs20A, 20B. Thus, the physical structure illustrated in FIGS. 1D, 1E canprovide the electrical connections illustrated in FIG. 5 .

Referring to the plan view and electrical schematic of FIG. 6 , firstLED 20A is electrically connected in serial with second LED 20B. LEDcontact pad 26 of cantilever portion 34 of first LED 20A is electricallyconnected to LED contact pad 26 of emission portion 33 of second LED 20Bwith LED electrode 28. LED contact pad 26 of cantilever portion 34 ofsecond LED 20B and LED contact pad 26 of emission portion 33 of firstLED 20A can be contacted by external power sources, for example throughelectrodes connected to them. LED electrode 28 is partially disposed ona portion of multi-LED native substrate 10 or a non-semiconductorstructure in semiconductor layer 30 between first and second LEDs 20A,20B. Emission portions 33 of first and second LEDs 20A, 20B areseparated by an LED emission separation distance LS less than acantilever length L. A third LED 20, or more LEDs 20, can be similarlyarranged on multi-LED native substrate 10 in alternating orientations ona side of second LED 20B opposite first LED 20A and electricallyconnected in serial with first and second LEDs 20A, 20B using additionalLED electrodes 28.

FIGS. 7A-7C illustrate other spatial arrangements of first LED 20A withrespect to second LED 20B on multi-LED native substrate 10. In thesearrangements, LED contact pads 26 that are not contacted by LEDelectrode 28 are farther apart so that they can be connected withcoarser, lower-resolution electrodes than LED electrode 28, reducing thecost of using multi-LED structures 99 in electronic or electro-opticalsystems. For example, multi-LED structures 99 can be constructed usinghigh-resolution photolithographic methods and materials found in theintegrated circuit or display arts and can be applied or used inlower-cost electronic or optical systems such as printed circuit boardsconstructed using lower cost methods and materials, for example found inthe printed circuit art.

For example, and as shown in FIG. 7A, multi-LED structures 99 cancomprise a first LED contact pad 26A disposed on first LED 20A and asecond LED contact pad 26B disposed on second LED 20B. First LED contactpad 26A and second LED contact pad 26B are separate from LED electrode28, that is LED electrode 28 is not electrically connected to first andsecond LED contact pads 26A, 26B and is therefore an open LED contactpad 26. An LED contact separation distance CS is the distance betweenthe centers of LED contact pads 26 in a direction parallel to a surfaceof multi-LED native substrate 10 and an LED length E is the longestdimension of LED 20 parallel to a surface of multi-LED native substrate10. According to some embodiments of the present disclosure, LED contactseparation distance CS between first LED contact pad 26A and second LEDcontact pad 26B is greater than (i) a first LED length E1 of first LED20A, (ii) a second LED length E2 of second LED 20B, or (iii) the largerof first LED length E1 and second LED length E2. Because LED contactseparation distance CS is greater than a length of an LED 20 or LEDseparation length LS, a lower-resolution and less-expensive process canbe used to construct electrical connections (wires or traces) to LEDcontact pads 26 (e.g., first and second LED contact pads 26A, 26B).

According to some embodiments of the present disclosure, and asillustrated in FIG. 7B, multi-LED native substrate 10 has an LED centerC, a first LED substrate edge 12A, and a second LED substrate edge 12Bdifferent from first LED substrate edge 12A. First LED contact pad 26Ais disposed a first distance Y1 closer to first LED substrate edge 12Athan to center C a second distance Y2. Second LED contact pad 26B isdisposed a first distance Y1 closer to second LED substrate edge 12Bthan to center C a second distance Y2. First LED substrate edge 12A andsecond LED substrate edge 12B can be on opposite edges of multi-LEDnative substrate 10, where multi-LED native substrate 10 has aquadrilateral surface, for example a rectangle.

According to some embodiments of the present disclosure and as shown inFIG. 7C, multi-LED native substrate 10 has an LED center C, a first LEDsubstrate corner 14A and a second LED substrate corner 14B differentfrom first LED substrate corner 14A. First LED contact pad 26A isdisposed closer to first LED substrate corner 14A a first distance X1than to center C a second distance X2 and second LED contact pad 26B isdisposed closer to second LED substrate corner 14B a first distance X1than to center C a second distance X2. First LED substrate corner 14Aand second LED substrate corner 14B can be on opposite corners ofmulti-LED native substrate 10, where multi-LED native substrate 10 is aquadrilateral, for example a rectangle. Because LED contact pads 26 aredisposed closer to first or second LED substrate edges 12A, 12B or firstor second LED substrate corners 14A, 14B than to LED centers C ofmulti-LED native substrate 10, a lower-resolution and less expensiveprocess can be used to construct electrical connections (wires ortraces) to LED contact pads 26.

FIG. 7D shows an illustrative multi-LED structure 99 arrangement havingfour LEDs 20 electrically connected in parallel (omitting a portion ofsecond LED electrode 28B). Any of LED 20 arrangements of FIGS. 5-7C orthose of FIGS. 8-23 can be extended to more than two LEDs 20 and can beelectrically connected in series, in parallel, or in combinations ofseries and parallel, as discussed with respect to FIGS. 27-30 .

First and second LEDs 20A, 20B arranged as illustrated in FIGS. 7A-7Ccan be electrically connected serially or in parallel as shown in FIGS.5 and 6 . In some embodiments, the portions connected by LED electrode28 are the same portion of first LED 20A and second LED 20B, for exampleboth cantilever portions 34 or both emission portions 33. In that case,first and second LEDs 20A, 20B are electrically connected in paralleland are separated by LED emission separation distance LS smaller thancantilever length L as shown in FIG. 5 . In some embodiments, theportion of first LED 20A connected by LED electrode 28 is different fromthe portion of second LED 20B connected by LED electrode 28. Forexample, if cantilever portion 34 of first LED 20A is connected by LEDelectrode 28 to emission portion 33 of second LED 20B (or vice versa),first and second LEDs 20A, 20B are electrically connected in serial andare separated by LED emission separation distance LS smaller thancantilever length L as shown in FIG. 6 . Regardless of LED 20arrangement, emission portions 33 are closer together than would be thecase for LEDs 20 separately constructed and disposed on separatesubstrates, especially for packaged LEDs, improving the appearance ofthe light emitted by LEDs 20 and improving manufacturing efficiency byreducing the number of micro-transfer steps necessary to construct amulti-LED pixel or lamp (illuminator).

The embodiments of the present disclosure illustrated in FIGS. 5-7D haveemission portions 33 separated by an LED emission separation distance LSthat is less than a cantilever length L of cantilever portion 34 andhave base portions 36 and cantilever portions 34 that extend in the samedirection and have a common midline. The embodiments illustrated inFIGS. 8-23 have base portions 36 and emission portions 33 that extend ina direction different from the direction of cantilever portions 34,forming an L shape where the different directions are orthogonal, forexample. In FIGS. 5-23 , emission portions 33 overlap base portions 36and can be labeled as such, as in FIGS. 5-6 . For clarity, base portions36 in FIGS. 8-23 are not labeled. LED 20 structures of FIGS. 3A-3C areused in FIGS. 8-21 but the structures of FIGS. 4A-4C could equally beused, or a combination thereof. L-shaped LEDs 20 as in FIGS. 8-21 canalso be combined with straight LEDs 20 as in FIGS. 5-7D.

As shown in FIGS. 8 and 11 , an L-shaped first LED 20A and an L-shapedsecond LED 20B are disposed on multi-LED native substrate 10 andelectrically connected in parallel. LED contact pad 26 of first emissionportion 33A of first LED 20A is electrically connected to LED contactpad 26 of second emission portion 33B of second LED 20B with first LEDelectrode 28A and LED contact pad 26 of first cantilever portion 34A offirst LED 20A is electrically connected to LED contact pad 26 of secondcantilever portion 34B of second LED 20B with second LED electrode 28B.As shown in FIGS. 9 and 10 , an L-shaped first LED 20A and an L-shapedsecond LED 20B are disposed on multi-LED native substrate 10 andelectrically connected in series. LED contact pad 26 of first emissionportion 33A of first LED 20A is electrically connected to LED contactpad 26 of second cantilever portion 34B of second LED 20B with LEDelectrode 28. In the embodiments of FIGS. 9 and 11 , first and secondLED lengths E1, E2 are less than LED contact separation distance CS (asshown in FIG. 7A, not indicated in FIGS. 9 and 11 ) providingwell-separated open LED contact pads 26 enabling lower-resolutionelectrical connections to open LED contact pads 26. The embodiments ofFIGS. 8-11 comprise first or second LEDs 20A, 20B that are mirrorreflections and rotations of each other and provide a compactarrangement of L-shaped first and second LEDs 20A and 20B in a multi-LEDstructure 99.

FIGS. 12-15 illustrate reflected and rotated arrangements of LEDs 20with greater LED contact pad 26 separation different from thearrangements of FIGS. 8-11 . Each of the embodiments of FIGS. 12-15comprise L-shaped first and second LEDs 20A, 20B electrically connectedwith LED electrode 28 that are rotated mirror images of each other. Theembodiments of FIGS. 12 and 15 are electrically connected in serial,since first emission portion 33A of first LED 20A is electricallyconnected to second cantilever portion 34B of second LED 20B, as in FIG.12 , and second emission portion 33B of second LED 20B is electricallyconnected to first cantilever portion 34A of first LED 20A, as in FIG.15 . The embodiments of FIGS. 13 and 14 are electrically connected inparallel, since first emission portion 33A of first LED 20A iselectrically connected to second emission portion 33B of second LED 20B,as in FIG. 13 , and first cantilever portion 34A of first LED 20A iselectrically connected to second cantilever portion 34B of second LED20B, as in FIG. 14 . All of the embodiments of FIGS. 12-15 providewell-separated open LED contact pads 26 enabling low-resolutionconnections to open LED contact pads 26 (as illustrated in FIG. 7A).

FIGS. 16-19 illustrate longer and narrower horizontal (or vertical)arrangements of LEDs 20 different from the arrangements of FIGS. 8-15 .Each of the embodiments of FIGS. 16-19 comprise L-shaped first andsecond LEDs 20A, 20B electrically connected with LED electrode 28 thatare rotated mirror images of each other. The embodiments of FIGS. 16 and17 are electrically connected in parallel, since first emission portions33A of first LED 20A are electrically connected to second emissionportions 33B of second LED 20B. The embodiments of FIGS. 18 and 19 areelectrically connected in serial, since first emission portions 33A offirst LED 20A are electrically connected to second cantilever portions34B of second LED 20B. The embodiments of FIGS. 17 and 19 providewell-separated open LED contact pads 26 enabling low-resolutionconnections to open LED contact pads 26 (e.g., as illustrated in FIG.7A).

FIGS. 20-23 illustrate longer and narrower horizontal (or vertical)mirror arrangements of LEDs 20 different from the arrangements of FIGS.8-19 . Each of the embodiments of FIGS. 20-23 comprise L-shaped firstand second LEDs 20A, 20B electrically connected with LED electrode 28that are rotated mirror images of each other. The embodiments of FIGS.20 and 23 are electrically connected in serial, since first emissionportion 33A of first LED 20A is electrically connected to secondcantilever portion 34B of second LED 20B, as in FIG. 20 , and secondemission portion 33B of second LED 20B is electrically connected tofirst cantilever portion 34A of first LED 20A, as in FIG. 23 . Theembodiments of FIGS. 21 and 22 are electrically connected in parallel,since first emission portion 33A of first LED 20A is electricallyconnected to second emission portion 33B of second LED 20B, as in FIG.21 , and first cantilever portion 34A of first LED 20A is electricallyconnected to second cantilever portion 34B of second LED 20B, as in FIG.22 . All of the embodiments of FIGS. 20-23 provide well-separated openLED contact pads 26 enabling low-resolution connections to open LEDcontact pads 26 (as illustrated in FIG. 7A).

Any mirror reflection, rotation, or mirror reflection and rotation aboutany axis, for example by 90, 180, or 270 degrees, of one or more of LEDs20 in any illustrated configuration of the present disclosure arecontemplated as embodiments of the present disclosure.

Any of the parallel-connected embodiments of FIGS. 5-23 can beconstructed and electrically connected using the configuration of FIGS.1D or 1E. In some such embodiments, open LED contact pads 26 can bedisposed anywhere suitable on multi-LED native substrate 10 separatefrom base portions 36 (and therefore emission portions 33) and can beseparated as described to provide electrical contacts that can beconnected using lower-resolution, coarse electrical connections (wires).

Multi-LED structures 99 of the present disclosure can be constructed ona native source wafer 40, for example a semiconductor or compoundsemiconductor wafer. As illustrated in FIG. 24A, a native source wafer40 comprises a sacrificial layer 42 having sacrificial portions 44separated by anchors 46. A multi-LED native substrate 10 is disposeddirectly over each sacrificial portion 44 and epitaxial layers 48disposed on sacrificial portion 44 with or without seed layers.Sacrificial portions 44 can be, for example, anisotropically etchableportions of sacrificial layer 42 or patterned layers of material thatare differentially etchable from multi-LED native substrate 10, such asoxide or nitride layers. Sacrificial portions 44 and anchor 46 ofsacrificial layer 42 can include a same material (e.g., anisotropicallyetchable material) and be defined, at least in part, by their relativeaccessibility to an etchant applied to native source wafer 40. Forexample, in some embodiments, and as illustrated in FIG. 24A, an etchantcan access sacrificial portions 44 through entry paths adjacent tomulti-LED structures 99 such that sacrificial portions 44 are etchedbefore the etchant reaches anchors 46. Epitaxial layers 48(semiconductor layer 30) can comprise one or more layers ofsemiconductor material, for example compound semiconductor materialssuch as GaN, GaAs, or InP with or without dopants and are patternedusing photolithographic methods and materials (e.g., by masked etchingwith patterned photoresist) to form separate semiconductor portions 30P.Any desired LED contact pads 26 are patterned, for example by depositingmetal such as aluminum or a transparent conductive oxide such as indiumtin oxide (e.g., by evaporation or sputtering) and patterning (e.g., byusing mask-exposure photoresist followed by etching) over semiconductorportions 30P. Patterned dielectric layers 24 can be deposited andpatterned (e.g., photolithographically patterned silicon dioxide orsilicon nitride) to insulate parts of semiconductor portions 30P. LEDelectrode(s) 28 are patterned, for example similarly to LED contact pads26, over multi-LED native substrate 10, patterned dielectric layers 24,and semiconductor portions 30P to form electrically connected LEDs 20.Sacrificial portions 44 can be etched to release multi-LED structure 99from native source wafer 40 so that multi-LED structure 99 is onlyattached to anchor 46 by LED structure tether 25. Multi-LED structure 99can then be transfer printed, for example micro-transfer printed.

FIG. 24A illustrates a multi-LED structure 99 that is micro-transferprintable directly from native source wafer 40 to a target substrate 70,shown in FIG. 25 . In some embodiments, for example as illustrated inFIG. 24B and further described in U.S. Pat. No. 10,224,231, multi-LEDnative substrate 10 does not include sacrificial layer 42 andsacrificial portions 44 as in FIG. 24A. Instead, patterned sacrificialportions 44 are deposited and patterned over multi-LED structure 99 andadhered with an adhesive layer 45 to a handle substrate 41 (handlewafer), native source wafer 40 is removed (e.g., by grinding or laserliftoff), and patterned sacrificial portions 44 etched away to releasemicro-transfer printable multi-LED structure 99 from handle substrate 41and adhesive layer 45 so that multi-LED structure 99 is only attached toanchor 46 by LED structure tether 25. Inverted multi-LED structure 99can then be micro-transfer printed to a desired target substrate 70, asshown in FIG. 25 . Similarly, any individual LEDs 20 can be disposed ontarget substrate 70 by micro-transfer printing in an inverted state.Micro-transfer printed LEDs 20 can comprise fractured or separatetethers 22 and multi-LED structures 99 can comprise fractured orseparated LED structure tethers 25 as a consequence of themicro-transfer printing process. Although not illustrated in FIG. 25 , acontroller (e.g., a pixel controller 66 as discussed with reference toFIGS. 27-30 below) can be disposed by micro-transfer printing ontotarget substrate 70 to control LEDs 20 and multi-LED structures 99 ontarget substrate 70 or onto multi-LED native substrate 10 to controlLEDs 20 of multi-LED structures 99.

According to some embodiments of the present disclosure and asillustrated in FIG. 24C, multi-LED native substrate 10 is provided as amesa 10M on native source substrate 40 and semiconductor layer 30 isdisposed on mesa 10M. When native source substrate 40 is removed (step230), mesa 10M (multi-LED native substrate 10) remains in place as aportion of multi-LED structure 99. For example, native source substrate40 and multi-LED native substrate 10 (and mesa 10M) can be sapphire.

Some embodiments of the present disclosure comprise both multi-LEDstructures 99 of FIGS. 1A-2C and multi-LED structures 99 of FIGS. 3A-4C,for example disposed on a component, pixel, display, or illuminationtarget substrate 70. Each multi-LED structure 99 can emit light of aspecific color, for example, red, green, or blue, since LEDs 20 in eachmulti-LED structure 99 can be formed in a common process with commonmaterials, for example a common epitaxial material such as compoundsemiconductor materials, like GaN, GaAs, or other LED materials, withsuitable doping, and therefore emit the same color of light. Amulti-color light-emitting device such as a pixel 60 or white-light lamp(illuminator) can comprise a multi-LED structure 99 with one or moreseparate, individual LEDs 20 or multiple different multi-LED structures99 and, optionally, one or more separate, individual LEDs 20 that emitdifferent colors of light. For example, and as shown in FIG. 25 , firstand second multi-LED structures 99A and 99B are disposed on targetsubstrate 70. Target substrate 70 can be any one or more of a componentsubstrate, pixel substrate, display substrate, or lamp (illuminator)substrate. First multi-LED structure 99A can emit a first color oflight, for example red, and multi-LED structure 99B can emit a secondcolor of light different from the first color of light, for examplegreen. Either or both of first and second multi-LED structures 99A and99B can comprise first and second LEDs 20A, 20B that are electricallyserially connected or electrically connected in parallel. In someembodiments, LEDs 20 of first multi-LED structure 99A are connected inseries and LEDs 20 of second multi-LED structure 99B are electricallyconnected in parallel. For example, red-light-emitting red LEDs 20R of ared multi-LED structure 99R can be electrically connected in series andgreen-light-emitting green LEDs 20G of a green multi-LED structure 99Gcan be electrically connected in parallel. A pixel 60 (for example usedin a display or lamp) can comprise multi-LED structures 99 andindividual LEDs 20, for example a blue-light-emitting blue LED 20B. Insome embodiments, a pixel 60 comprises a series-connected set ofdifferent light-emitters that emit different colors of light, forexample a red-light emitter, a green-light emitter, and a blue-lightemitter controlled by a single control signal. Any one or more of theseries-connected set of red-light emitter, green-light emitter, orblue-light emitter can be individual LEDs 20 or multi-LED structures 99.The series-connected set of light-emitters can be separately controlledfrom the colored-light emitters and together emit white light, and thewhite-point color of pixel 60 can be adjusted by controlling theluminance of the red, green, or blue light-emitters (e.g., LEDs 20 ormulti-LED structures 99) with respect to the white color of lightemitted by the series-connected set of light emitters.

Thus, embodiments of the present disclosure provide multi-LED structures99 that, used individually, enable light-emitting products that aresmaller in area, are more highly integrated, and are more efficientlyincorporated in products by using micro-transfer printing. Moreover,devices using groups of multi-LED structures 99 and LEDs 20 that emitdifferent colors of light can also have improved electrical powerefficiency. Such devices can be, for example, displays or lamps(illuminators).

According to embodiments of the present disclosure, by providingseries-connected multiple differently colored LEDs 20 that emitdifferent colors of light controlled by a common control signal (e.g.,to emit white light), a higher voltage can be applied to LEDs 20,improving power distribution and operating voltage to pixels 60 andreducing system power losses. For example, a series-connected set oflight emitters with a red-light-emitting red LED 20R, agreen-light-emitting green LED 20G, and a blue-light-emitting blue LED20B can be operated at 8 volts, as can a series-connected four-LEDmulti-LED structure 99 of red-light-emitting red LEDs 20R (or twoseries-connected red-light-emitting multi-LED structures 99 comprisingtwo red LEDS 20R), a series-connected two-LED (or three-LED) multi-LEDstructure 99 of green-light-emitting green LEDs 20G, and aseries-connected three-LED multi-LED structure 99 of blue-light-emittingblue LEDs 20B.

Referring to FIG. 26 , according to some embodiments of the presentdisclosure, LEDs 20 that each emit a different color of light, forexample red LED 20R that emits red light, green LED 20G that emits greenlight, and blue LED 20B that emits blue light, have differentlight-output efficiencies with respect to current density for therespective LEDs 20. According to some embodiments, different LEDs 20 canalso have different preferred driving voltages, for example a forwardvoltage across the diode. As shown in FIG. 26 , blue LED 20B has a blueefficiency vs. current density 71, green LED 20G has a green efficiencyvs. current density 72, and red LED 20R has a red efficiency vs. currentdensity 73 illustrated by the labeled lines of the graph. Blueefficiency vs. current density 71 has a blue efficiency maximum 71M,green efficiency vs. current density 72 has a green efficiency maximum72M, and red efficiency vs. current density 73 has an approximate redefficiency maximum 73M (that can be at a greater current density than isshown in FIG. 26 , given the limited data set acquired and plotted inFIG. 26 ).

As shown in FIG. 26 , green LED 20G has green efficiency maximum 72M ata lower current density than blue efficiency maximum 71M. Both blue andgreen efficiency maximums 71M and 72M are at a lower current densitythan red efficiency maximum 73M. Green efficiency maximum 72M is at acurrent or current density that is approximately one half of blueefficiency maximum 71M. Therefore, if current is supplied to both asingle blue LED 20B and a multi-LED structure 99 comprising two greenLEDs 20G electrically connected in parallel (e.g., as shown in FIGS. 1A,1B, 5, 8, 11 and others) at blue efficiency maximum 71M, the electricalcurrent that passes through each green LED 20G will be one half theelectrical current that passes through blue LED 20B and the currentdensity passing through green LED 20G will likewise be one half that ofthe current density passing through blue LED 20B. In this configuration,both blue LED 20B and green LED 20G can operate at approximately maximumefficiency while using the same current supplied by a common currentsupply, improving their efficiency in a display or lamp 80 (as discussedfurther below with respect to FIGS. 27-30 ). (Both current and currentdensity are referenced since, if LEDs 20 are the same size, current andcurrent density are directly related.)

As shown in FIG. 26 , red LED 20R is less efficient than blue or greenLEDs 20B, 20G at a given current density. Moreover, according to someembodiments, red LEDs 20R can operate at a lower voltage than blue orgreen LEDs 20B, 20G. For example, blue-light-emitting compoundsemiconductor materials can emit light at voltages ranging from 2.5-3.7volts, green-light-emitting compound semiconductor materials can emitlight at voltages ranging from 1.9-4 volts, and red-light-emittingcompound semiconductor materials can emit light at voltages ranging from1.6-2 volts. Thus, blue and green LEDs 20B, 20G can operate effectivelyat a common voltage (e.g., 3.6 volts) but red LEDs 20R can require adifferent voltage. Providing such different voltages can requireadditional control or power circuitry in a display or lamp 80.Therefore, according to embodiments of the present disclosure, red LEDs20R are provided in a series connected red multi-LED structure 99R usedin a display, lamp, or indicator so that the driving voltage of redmulti-LED structure 99R is greater than that of a single red LED 20Rtherein. Consequently, each red LED 20R in a red multi-LED structure 99Rcan be operated more efficiently by providing a more optimized drivingvoltage even while red multi-LED structure 99R itself is driven at thesame voltage as parallel connected green and blue LEDs 20G, 20B.

According to some embodiments of the present disclosure and asillustrated in FIG. 27 , a display or lamp controller 50 or pixelcontroller 66 supplies pixels 60 and red, green, and blue LEDs 20R, 20G,20B with a common voltage. For example, if two red LEDs 20R areconnected in series at a given voltage, each of red LEDs 20R can bedriven at one half the given voltage. For example, if 3.6 volts isprovided to blue, green, and red

LEDs 20B, 20G, 20R, blue and green LEDs 20B, 20G can be driven at 3.6volts and two red LEDs 20R are each driven at 1.8 volts because they areelectrically connected in series. Furthermore, if two sets of LEDs 20 asdescribed are electrically connected in series, doubling the drivingvoltage to 7.2-8 volts, the driving voltage can be approximately equalto the voltage used to drive series-connected red, green, and blue LEDs20R, 20G, 20B. Green LEDs 20G can be connected in parallel as part of agreen multi-LED structure 99G and red LEDs 20R can be connected inseries as part of a red multi-LED structure 99R. Therefore, according toembodiments of the present disclosure, providing a higher voltage colorlight-emitting system (e.g., a display or lamp 80) and using series- andparallel-connected multi-LED structures 99 and LEDs 20 increases systempower efficiency and also increases LED 20 light-emitting efficiency byoptimizing LED driving voltage and current density, and thereforeexternal quantum efficiency.

A matrix-addressed display 80 (or lamp 80) with pixels 60 usingmulti-LED structures 99 is illustrated in FIGS. 27-30 . As shown inthese Figures, pixels 60 are arranged in a pixel array 68 on a displayor lamp substrate 82 or any other desired substrate. Embodiments of thepresent disclosure are not limited to display or lamp applications. Eachpixel 60 comprises a pixel controller 66 driven by a power/voltagesignal 54, ground 56, and control signals 52 (e.g., a row control signaland a column control signal). As shown in FIG. 27 , each pixel 60comprises a blue sub-pixel 63 comprising a blue LED 20B, a greensub-pixel 62 comprising a green multi-LED structure 99G having greenLEDs 20G electrically connected in parallel, and a red sub-pixel 61comprising a red multi-LED structure 99R having red LEDs 20Relectrically connected in series. Red, green, and blue sub-pixels 61,62, 63 can be driven at a common voltage and with more efficient currentdensity and quantum efficiency.

As shown in FIG. 28 , blue sub-pixel 63 can comprise one blue LED 20B,green sub-pixel 62 can comprise three green LEDs 20G electricallyconnected in parallel in one green multi-LED structure 99G, and redsub-pixel 61 can comprise three red LEDs 20R electrically connected inseries in one red multi-LED structure 99R. Such arrangements of LEDs 20and multi-LED structures 99 can improve system power efficiency.

As illustrated in the embodiment of FIG. 29 , blue sub-pixel 63 cancomprise two blue-light-emitting blue LEDs 20B in a blue multi-LEDstructure 99B. Green sub-pixel 62 can comprise four green LEDs 20G inone or two green multi-LED structures 99G that emit green light. Forexample, four green LEDs 20G can be electrically connected in series andparallel in one green multi-LED structure 99G as shown, twoseries-connected green multi-LED structures 99G each comprising twogreen LEDs 20G connected in parallel, or two parallel-connected greenmulti-LED structures 99G each comprising two green LEDs 20G connected inseries. Red sub-pixel 61 can comprise four red LEDs 20R electricallyconnected in series that emit red light in one red multi-LED structure99R or two series-connected red multi-LED structures 99R each comprisingtwo red LEDs 20R electrically connected in series.

As illustrated in the embodiment of FIG. 30 , red, green, and bluesub-pixels 61, 62, 63 can be connected as illustrated in FIG. 29 . Inaddition, a white-light emitting white sub-pixel 64 comprises aseries-connected combination of red, green, and blue LEDs 20R, 20G, 20Bthat together emit white light. Red, green, blue, and white sub-pixels61, 62, 63, 64 can be driven at a common voltage greater than thedriving voltage of at least one and, in some embodiments any, single LED20 and each of the color sub-pixels are controlled with approximatelytheir best light-emitting efficiency. Such an arrangement, as in FIG. 29, can use double the driving voltage and consequently reduce powerlosses in a display or lamp 80 system.

As shown in FIG. 31 , a display or lamp 80 according to embodiments ofthe present disclosure can comprise a pixel array 68 of pixels 60disposed on a display or lamp substrate 82 and controlled by controller50 with power and ground signals 54, 56 and control signals 52. Eachpixel 60 comprises red, green, and blue sub-pixels 61, 62, 63 (andoptionally white sub-pixel 64, not shown) disposed on a target (pixel)substrate 70 and comprises one or more multi-LED structures 99 and,optionally, LEDs 20, for example as illustrated in any of FIGS. 25 and27-30 . FIG. 32 is a schematic structural perspective of the structureof FIG. 31 with the addition of a pixel controller 66 and without theelectrical connections indicated in FIG. 31 . In some embodiments, pixel60 is an active-matrix pixel with a pixel controller 66. In someembodiments, pixel 60 is a passive-matrix pixel and does not include apixel controller 66 (not shown).

In some embodiments of the present disclosure and as illustrated in FIG.33 , multi-LED structures 99 comprise at least one LED 20 biased in aforward direction and one LED 20 biased in an opposite direction. Asshown in FIG. 33 , first LED 20A is biased in one direction, indicatedby the ‘+’ symbol on emission portion 33 and ‘−’ symbol on cantileverportion 34 and second LED 20B is biased in an opposite direction,indicated by the ‘+’ symbol on cantilever portion 34 and ‘−’ symbol onemission portion 33. Thus, if multi-LED structure 99 is driven by analternating current, multi-LED structure 99 can emit light in bothpositive and negative cycles, alternately from first LED 20A and secondLED 20B.

As shown in FIG. 34 , additional non-native LEDs 20 can be disposed onmulti-LED native substrate 10 of multi-LED structure 99, for example bymicro-transfer printing the additional LEDs 20 onto multi-LED nativesubstrate 10. The additional LED 20 and native first and second LEDs20A, 20B of multi-LED structure 99 can be electrically connected in acommon step with common materials.

Furthermore, according to some embodiments, a multi-LED structure 99 cancomprise additional multi-LED structures 99 disposed on multi-LED nativesubstrate 10, as shown in FIG. 35 with first multi-LED structure 99Acomprising first multi-LED native substrate 10A and second multi-LEDstructure 99B comprising second multi-LED native substrate 10B, disposedon first multi-LED native substrate 10A, together with additional LEDs20. LEDs 20 of multi-LED structure 99 and any LEDs 20 disposed directlyon multi-LED native substrate 10 can comprise a semiconductor materialdifferent from the semiconductor material of semiconductor layer 30, forexample so that the different LEDs 20 can emit different colors of lightand form a display pixel 60 or lamp light-emitter. Thus, all of LEDs 20of an entire pixel 60 or multi-color emitter (e.g., as shown in FIGS.27-30 ), possibly including additional multi-LED structures 99 can bedisposed on a multi-LED native substrate 10 and can be a micro-transferprintable structure. For example, FIG. 35 illustrates a series-connectedred-light-emitting red multi-LED structure 99R (e.g., as shown in FIGS.6, 9 ) with a green-light-emitting green multi-LED structure 99G (e.g.,as shown in FIGS. 5, 8 ) disposed on first multi-LED native substrate10A of red multi-LED structure 99R together with a blue-light-emittingblue LED 20B (electrically connected as shown in FIG. 27 ) and aseries-connected white-light sub-pixel 64 comprising a red LED 20R, agreen LED 20G, and a blue LED 20B (electrically connected as shown inFIG. 30 ) to construct a pixel 60. In an active-matrix embodiment, pixelcontroller 66 can also be micro-transfer printed to first multi-LEDnative substrate 10A (not shown).

According to embodiments of the present disclosure and as illustrated inFIG. 36 , a method of making a multi-LED structure 99 comprisesproviding a native source wafer 40 with sacrificial portions 44 in step100, disposing a single, unitary, and contiguous multi-LED nativesubstrate 10 in step 110 with or without a seed layer directly on orover sacrificial portions 44, disposing semiconductor layers 30 onmulti-LED native substrate 10 in step 120, and patterning semiconductorlayers 30 in step 130 to form spatially separated semiconductor portions30P, semiconductor portions 30P defining at least a first LED 20A and asecond LED 20B separate from first LED 20A. First LED 20A and second LED20B each comprise (i) a first layer 31 having a cantilever portion 34and a base portion 36, and (ii) a second layer 32 disposed only overbase portion 36 of first layer 31 forming emission portion 33. In someembodiments, cantilever portion 34 of first LED 20A extends in a firstdirection D1 and base portion 36 of first LED 20A extends in a seconddirection D2 different from first direction D1. In some embodiments,cantilever portion 34 of first LED 20A has a first cantilever length L1,cantilever portion 34 of second LED 20B has a second cantilever lengthL2, and an LED emission separation distance LS between a light-emittingarea of first LED 20A emission portion 33 and a light-emitting area ofsecond LED 20B emission portion 33 is less than or equal to firstcantilever length L1 or less than or equal to second cantilever lengthL2, and in some embodiments, both are true.

In step 140, an LED electrode 28 is disposed on at least a portion ofmulti-LED native substrate 10 or a non-semiconductor structure insemiconductor first layer 31 (e.g., a patterned dielectric layer 24, anddisposed on at least a portion of first LED 20A and on at least aportion of second LED 20B so that LED electrode 28 electrically connectsfirst LED 20A to second LED 20B.

According to some embodiments, sacrificial portions 44 are etched torelease multi-LED structures 99 from native source wafer 40 in step 150,a stamp is provided in step 160, a target substrate 70 is provided instep 170, and multi-LED structures 99 are micro-transfer printed fromnative source wafer 40 to target substrate 70 with the stamp in step180. This process corresponds to the native source wafer structure ofFIG. 24A. In the illustrative method of FIG. 36 , multi-LED structures99 can be disposed by a stamp on display or lamp substrate 82 with firstlayer 31 between second layer 32 and display or lamp substrate 82 (ortarget substrate 70) so that first layer 31 is on or adjacent to displayor lamp substrate 82. If an inverted printed multi-LED structures 99with second layer 32 between first layer 31 and display or lampsubstrate 82 is desired, a second stamp can remove multi-LED structures99 from the stamp that retrieved multi-LED structures 99 from nativesource wafer 40 and then print them to display or lamp substrate 82.

According to embodiments of the present disclosure and as illustrated inFIG. 37 , a method of making a multi-LED structure 99 comprisesproviding a native source wafer 40 in step 100A, disposing single,unitary, and contiguous multi-LED native substrate 10 in step 110 withor without a seed layer, disposing semiconductor layers 30 on multi-LEDnative substrate 10 in step 120, and patterning semiconductor layers 30in step 130 to form spatially separated semiconductor portions 30P, thesemiconductor portions 30P defining at least a first LED 20A and asecond LED 20B separate from first LED 20A. First LED 20A and second LED20B each comprise (i) a first layer 31 having a cantilever portion 34and a base portion 36, and (ii) a second layer 32 disposed only overbase portion 36 of first layer 31 forming emission portion 33. In someembodiments, cantilever portion 34 of first LED 20A extends in a firstdirection D1 and base portion 36 of first LED 20A extends in a seconddirection D2 different from first direction D1. In some embodiments,cantilever portion 34 of first LED 20A has a first cantilever length L1,cantilever portion 34 of second LED 20B has a second cantilever lengthL2, and an LED emission separation distance LS between a light-emittingarea of first LED 20A emission portion 33 and a light-emitting area ofsecond LED 20B emission portion 33 is less than or equal to firstcantilever length L1 or less than or equal to second cantilever lengthL2, and in some embodiments, both are true.

In step 140, an LED electrode 28 is disposed on at least a portion ofsingle, unitary, and contiguous multi-LED native substrate 10 ornon-semiconductor structure in semiconductor layer 30 and disposed on atleast a portion of first LED 20A and on at least a portion of second LED20B, LED electrode 28 electrically connecting first LED 20A to secondLED 20B.

In step 200, sacrificial portions 44 (release layers) are disposed andpatterned over LED 20, a handle substrate 41 is provided in step 210,and in step 220 handle substrate 41 is adhered to sacrificial portions44 with adhesive layer 45. In step 230, native source wafer 40 isremoved, e.g., by grinding or laser lift-off, leaving multi-LEDstructure 99 adhered with adhesive layer 45 to handle substrate 41.

According to some embodiments, sacrificial portions 44 are etched torelease multi-LED structures 99 from native source wafer 40 in step150A, a stamp is provided in step 160, a target substrate 70 is providedin step 170, and multi-LED structures 99 are micro-transfer printed fromnative source wafer 40 to target substrate 70 with the stamp in step180. This process corresponds to the native source wafer structure ofFIG. 24B. In the illustrative method of FIG. 37 , multi-LED structures99 can be disposed by a stamp on display or lamp substrate 82 (targetsubstrate 70) in an inverted arrangement with second layer 32 betweenfirst layer 31 and display or lamp substrate 82 so that second layer 32is on or adjacent to display or lamp substrate 82. If a non-invertedprinted multi-LED structures 99 with first layer 31 between second layer32 and display or lamp substrate 82 is desired, a second stamp canremove multi-LED structures 99 from the stamp that retrieved multi-LEDstructures 99 from native source wafer 40 and then print them to displayor lamp substrate 82.

The arrangements of LEDs 20 and multi-LED structures 99 in FIGS. 27-30can improve system power efficiency by using a common (and optionallygreater) voltage for the sub-pixels and electrically connecting LEDs 20and multi-LED structures 99 to match current densities and quantumefficiencies of sub-pixels to LED 20 characteristics for approximatelybest efficiencies. For example, in embodiments comprising LEDs 20 havingthe characteristics illustrated in FIG. 26 , a driving voltage can beapproximately 8 volts or in a range of 7 to 9 volts while operatingindividual LEDs 20 at approximately their most efficient current densityand voltage.

In some embodiments of the present disclosure, LEDs 20 are inorganiclight-emitting diodes. As used herein, two LEDs 20 that are seriallyconnected are two LEDs 20 that are electrically connected in serial, sothat the first terminal of an LED 20 is electrically connected to thesecond terminal of another LED 20. The remaining two terminals areelectrically connected to common voltage signal 54 or common groundsignal 56 and a control signal 52, for example provided by controller 50or pixel controller 66. The first terminals of two LEDs 20 that areelectrically connected in parallel are connected together and the secondterminals of the two parallel-connected LEDs 20 are likewise connectedtogether. The first and second terminals are electrically connected tocommon voltage signal 54 or common ground signal 56 and a control signal52, for example provided by pixel controller 66. Both LEDs 20 can bebiased in the same forward direction.

According to embodiments of the present disclosure, display or lampsubstrate 82 is a substrate having substantially parallel and opposingsides, on one of which target substrates 70 are disposed for example bysurface mount techniques. In some embodiments, LEDs 20 and multi-LEDstructures 99 are disposed directly on display or lamp substrate 82, forexample by micro-transfer printing. Display or lamp substrate 82 can bea glass, polymer, ceramic, or metal substrate having at least one sidesuitable for constructing electrical conductors. Display or lampsubstrate 82 or target substrate 70 can have a thickness from 5 micronsto 20 mm (e.g., 5 to 10 microns, 10 to 50 microns, 50 to 100 microns,100 to 200 microns, 200 to 500 microns, 500 microns to 0.5 mm, 0.5 to 1mm, 1 mm to 5 mm, 5 mm to 10 mm, or 10 mm to 20 mm) and can be, but isnot necessarily, transparent (e.g., at least 50%, at least 70%, at least80%, or at least 90% transparent to visible light).

Common power and ground signals 54, 56 can be made usingphotolithographic, printed circuit board, inkjet, or display techniquesand materials, for example using copper, aluminum, or silver materialsto form patterned electrical conductors that conduct electrical control52 and power signals 54 to pixels 60 to enable pixels 60 to displayinformation or emit light, for example for an image, illuminator (lamp),or indicator. The electrical conductors can be electrically conductivemetal wires formed, or disposed on, display or lamp substrate 82 using,for example, photolithographic methods, tools, and materials. Similarly,electrodes can be made using photolithographic methods, tools, andmaterials.

Target substrate 70 can also be glass or plastic or can be asemiconductor, such as silicon. Target substrate 70 can be transparentor opaque and, if transparent, light emitted from LEDs 20 can betransmitted through target substrate 70, depending on the orientation ofLEDs 20 (e.g., top-emitting or bottom-emitting).

Native source wafers 40 can be compound semiconductor or silicon wafersand patterned sacrificial layer 42, LED structure tethers 25, and LEDs20 can be made using photolithographic methods and materials found inthe integrated circuit industries. For example, a source wafer can beGaN, InGaN, or GaAs. Inorganic light-emitting diodes 20 can be made in asemiconductor material, such as a compound semiconductor (e.g., GaN orGaAs, with or without doping). The semiconductor material can becrystalline. Any one or each of LEDs 20 can have at least one of a widthfrom 2 to 50 μm (e.g., 2 to 5 μm, 5 to 10 μm, 10 to 20 μm, or 20 to 50μm), a length from 2 to 50 μm (e.g., 2 to 5 μm, 5 to 10 μm, 10 to 20 μm,or 20 to 50 μm), and a height from 2 to 50 μm (e.g., 2 to 5 μm, 5 to 10μm, 10 to 20 μm, or 20 to 50 μm).

In some embodiments, in operation, power 54, ground 56, and controlsignals 52 (e.g., row signals and column signals) are applied toelectrical conductors on display or lamp substrate 82. The electricalconductors on display or lamp substrate 82 are in electrical contactwith multi-LED structure 99 and any other LEDs 20 and supply electricalpower at a desired voltage to common power signal 54, supply anelectrical ground to common ground signal 56, and supply control signals52 to multi-LED structures 99 and LEDs 20. The ground 56, voltage 54,and control signals 52 are electrically conducted through LED electrodes28 and electrodes formed on target substrate 70 an any display or lampsubstrate 82 to LEDs 20, any pixel controller 66, and any display orlamp controller 50 to control LEDs 20 and multi-LED structures 99 toemit light.

Methods of forming useful micro-transfer printable structures aredescribed, for example, in the U.S. Pat. 8,889,485. For a discussion ofmicro-transfer printing techniques see, U.S. Pat. Nos. 8,722,458,7,622,367 and 8,506,867, the disclosures of which are herebyincorporated by reference in their entirety. Micro-transfer printingusing compound micro-assembly structures and methods can also be usedwith the present disclosure, for example, as described in U.S. patentapplication Ser. No. 14/822,868, filed Aug. 10, 2015, entitled CompoundMicro-Assembly Strategies and Devices, the disclosure of which is herebyincorporated by reference in its entirety. In some embodiments, pixel 60is a compound micro-assembled device.

Micro-transfer printable elements can be constructed using foundryfabrication processes used in the art. Layers of materials can be used,including materials such as metals, oxides, nitrides and other materialsused in the integrated-circuit art. Multi-LED structures 99 can havedifferent sizes, for example, of no more than 1000 square microns,10,000 square microns, 100,000 square microns, or 1 square mm, orlarger, and can have variable aspect ratios, for example at least 1:1,2:1, 5:1, or 10:1. Multi-LED structures 99 and multi-LED nativesubstrate 10 can be rectangular or can have other shapes.

Native source wafers 40 and multi-LED structures 99, micro-transferprinting stamps, target substrates 70, and display or lamp substrates 82can be made separately and at different times or in different temporalorders or locations and provided in various process states.

As is understood by those skilled in the art, the terms “over” and“under” are relative terms and can be interchanged in reference todifferent orientations of the layers, elements, and substrates includedin the present disclosure. For example, a first layer on a second layer,in some implementations means a first layer directly on and in contactwith a second layer. In other implementations a first layer on a secondlayer includes a first layer and a second layer with another layertherebetween.

Having described certain implementations of embodiments, it will nowbecome apparent to one of skill in the art that other implementationsincorporating the concepts of the disclosure may be used. Therefore, thedisclosure should not be limited to certain implementations, but rathershould be limited only by the spirit and scope of the following claims.

Throughout the description, where apparatus and systems are described ashaving, including, or comprising specific components, or where processesand methods are described as having, including, or comprising specificsteps, it is contemplated that, additionally, there are apparatus, andsystems of the disclosed technology that consist essentially of, orconsist of, the recited components, and that there are processes andmethods according to the disclosed technology that consist essentiallyof, or consist of, the recited processing steps.

It should be understood that the order of steps or order for performingcertain action is immaterial so long as the disclosed technology remainsoperable. Moreover, two or more steps or actions in some circumstancescan be conducted simultaneously. The disclosure has been described indetail with particular reference to certain embodiments thereof, but itwill be understood that variations and modifications can be effectedwithin the spirit and scope of the claimed invention.

PARTS LIST

A cross section line

B cross section line

C LED center

CS LED contact separation distance

D1 first direction

D2 second direction

E LED length

E1 first LED length

E2 second LED length

L cantilever length

L1 first cantilever length

L2 second cantilever length

LS LED emission separation distance

X1, Y1 first distance

X2, Y2 second distance

10 multi-LED native substrate

10A first multi-LED native substrate

10B second multi-LED native substrate

10M multi-LED native substrate mesa

12A first LED substrate edge

12B second LED substrate edge

14A first LED substrate corner

14B second LED substrate corner

20 LED

20A first LED

20B second LED/blue LED

20R red LED

20G green LED

22 LED tether

24 patterned dielectric layer

25 LED structure tether

26 LED contact pad

26A first LED contact pad

26B second LED contact pad

28 LED electrode

28A first LED electrode

28B second LED electrode

30 semiconductor layer

30A first semiconductor portion

30B second semiconductor portion

30P semiconductor portion

31 first layer

32 second layer

33 emission portion

33A first emission portion

33B second emission portion

34 cantilever portion

34A first cantilever portion

34B second cantilever portion

36 base portion

38 recombination zone

39 conduction zone

40 native source wafer

41 handle wafer

42 patterned sacrificial layer

44 sacrificial portion

45 adhesive layer

46 anchor

48 epitaxial layers

50 display controller/lamp controller

52 control signal

54 power/voltage signal

56 ground

60 pixel

61 red sub-pixel

62 green sub-pixel

63 blue sub-pixel

64 white sub-pixel

66 pixel controller

68 pixel array

70 target substrate

71 blue efficiency vs. current density

71M blue efficiency maximum

72 green efficiency vs. current density

72M green efficiency maximum

73 red efficiency vs. current density

73M red efficiency maximum

80 display/lamp

82 display substrate/lamp substrate

99 multi-LED structure

99A first multi-LED structure

99B second multi-LED structure/blue multi-LED structure

99G green multi-LED structure

99R red multi-LED structure

100 provide native source wafer with sacrificial portions step

100A provide native source wafer with sacrificial portions step

110 dispose multi-LED native substrate step

120 dispose semiconductor layer over sacrificial portions step

130 pattern semiconductor layer step

140 dispose electrode step

150 etch sacrificial portions step

150A etch sacrificial portions step

160 provide stamp step

170 provide target substrate step

180 micro-transfer print multi-LED structure step

200 form sacrificial portions step

210 provide handle substrate step

220 adhere handle substrate step

230 remove native source wafer step

1-27. (canceled)
 28. A multi-LED component structure, comprising: acomponent substrate; a first multi-LED native substrate disposed on thecomponent substrate, the first multi-LED native substrate having a firstLED and a separate second LED disposed thereon, wherein the first LEDand the second LED are native to the first multi-LED native substrateand electrically connected; and a second multi-LED native substratehaving a third LED and a separate fourth LED disposed thereon, the thirdLED and the fourth LED are native to the second multi-LED nativesubstrate and electrically connected, wherein the first LED, the secondLED, the third LED, and the fourth LED are electrically connected to acommon electrical connection.
 29. The multi-LED component structure ofclaim 28, wherein at least one of (i) the first LED and the second LEDare electrically connected in series and the third LED and the fourthLED are electrically connected in parallel and (ii) the first LED andthe second LED emit a first color of light and the third LED and thefourth LED emit a second color of light.
 30. The multi-LED componentstructure of claim 28, wherein the second multi-LED native substrate isdisposed on the first multi-LED native substrate.
 31. The multi-LEDcomponent structure of claim 28, further comprising a fifth LEDnon-native to the component substrate, the first multi-LED nativesubstrate and the second multi-LED native substrate, wherein the fifthLED emits a different color of light from the first LED, the second LED,the third LED, and the fourth LED.
 32. (canceled)
 33. A method of makinga multi-LED structure, the method comprising: providing a multi-LEDnative substrate; disposing semiconductor layers on the multi-LED nativesubstrate; patterning the semiconductor layers to form spatiallyseparated semiconductor portions, the semiconductor portions defining atleast a first LED and a second LED separate from the first LED, thefirst LED and the second LED each comprising (i) a first layer having acantilever portion and a base portion, and (ii) a second emission layerdisposed only over the base portion of the first layer; and disposing anLED electrode on at least a portion of the multi-LED native substrate ora non-semiconductor structure in the semiconductor layer, the LEDelectrode electrically connecting the first LED to the second LED,wherein (i) the cantilever portion of the first LED extends in a firstdirection and the base portion of the first LED extends in a seconddirection different from the first direction, (ii) the cantileverportion of the first LED has a first cantilever length, the cantileverportion of the second LED has a second cantilever length, and an LEDemission separation distance between the emission portion of the firstLED and the emission portion of the second LED is less than or equal tothe first cantilever length and less than or equal to the secondcantilever length, or (iii) both (i) and (ii).
 34. The method of claim33, comprising: providing an LED source wafer comprising sacrificialportions separated by anchors, wherein a multi-LED structure is disposedentirely and completely over each sacrificial portion and each multi-LEDstructure is physically connected to an anchor of the anchors with atether; etching the sacrificial portions to suspend each multi-LEDstructure over a corresponding sacrificial portion; providing a stampand a target substrate; and micro-transfer printing each multi-LEDstructure from the multi-LED native substrate to the target substratewith the stamp.
 35. (canceled)
 36. An LED wafer, comprising a wafercomprising sacrificial portions separated by anchors, wherein amulti-LED component structure according to claim 28 is disposed entirelyand completely over each sacrificial portion and each multi-LEDcomponent structure is physically connected to an anchor of the anchorswith a tether.
 37. The multi-LED component structure of claim 28,comprising an LED electrode disposed on at least a portion of the firstLED and on at least a portion of the second LED, wherein the LEDelectrode is disposed on at least a portion of the first multi-LEDnative substrate.
 38. The multi-LED component structure of claim 28,wherein the first LED and the second LED are electrically connected inserial.
 39. The multi-LED component structure of claim 28, wherein thefirst LED and the second LED are electrically connected in parallel. 40.The multi-LED component structure of claim 28, wherein the first LED andthe second LED have any one or combination of (i) substantially the samesize, (ii) substantially the same area over the multi-LED substrate, and(iii) substantially the same light-emitting area.
 41. The multi-LEDcomponent structure of claim 28, comprising an LED structure tether. 42.The multi-LED component structure of claim 28, wherein any one orcombination of (i) the multi-LED native substrate has a surface and thefirst direction is orthogonal to the second direction and both the firstand the second directions are substantially parallel to the surface,(ii) at least a portion of the first LED and at least a portion of thesecond LED extend in substantially a same direction, and (iii) at leasta portion of the first LED and at least a portion of the second LEDextend in substantially orthogonal directions.
 43. The multi-LEDcomponent structure of claim 28, comprising an LED electrode disposed onat least a portion of the first LED and on at least a portion of thesecond LED, the LED electrode electrically connecting the first LED tothe second LED.
 44. The multi-LED component structure of claim 43,comprising a first LED contact disposed on the first LED and a secondLED contact disposed on the second LED, wherein the first LED contactand the second LED contact are spatially separated from the LEDelectrode.
 45. The multi-LED component structure of claim 44, wherein anLED contact separation distance between the first LED contact and thesecond LED contact is greater than (i) a first LED length of the firstLED, (ii) a second LED length of the second LED, or (iii) the larger ofthe first LED length and the second LED length.
 46. The multi-LEDcomponent structure of claim 28, wherein the first LED and the secondLED each comprise a different semiconductor material from the third LEDand the fourth LED.
 47. The multi-LED component structure of claim 28,comprising one or more LEDs separate from the first LED and separatefrom the second LED disposed on the first multi-LED native substrate,wherein the first and second LEDs comprise a different semiconductormaterial from the one or more LEDs and the one or more LEDs arenon-native to the first multi-LED substrate.
 48. The multi-LED componentstructure of claim 28, comprising one or more LEDs separate from thefirst LED and separate from the second LED disposed on the firstmulti-LED native substrate, wherein the first and second LEDs comprise adifferent semiconductor material from the one or more LEDs and the oneor more LEDs are non-native to the first multi-LED substrate.
 49. Themulti-LED component structure of claim 28, wherein the first multi-LEDnative substrate comprises at least a portion of the first layer or thefirst layer comprises at least a portion of the first multi-LED nativesubstrate and the first multi-LED native substrate is electricallyconductive.